In _A. cardamines_ the orange flush has overflowed the discoidal spot, as it were, in the male, and is absent in the female. But in _A. eupheno_ we have an intermediate state, for as the figures show, in the female, Fig. 8, the orange tip only extends half-way to the discoidal spot, and in the male it reaches it. Moreover it is to be noticed that the flow of colour, to continue the simile, is unchecked by the spot in _cardamines_, but where the spot has expanded to a bar in _eupheno_ it has dammed the colour up and ponded it between bar and tip. An exactly intermediate case between these two species is seen in _A. euphemoides_, Fig. 10, Plate IV., in which the spot is elongated, and dribbles off into an irregular band, into which the orange has trickled, as water trickles through imperfect fascines. This series of illustrations might be repeated in almost any group of butterflies, but sufficient has been said to show how spots can spread into patches, either by the spreading of one or by the coalescence of several. We will now take an illustration of the formation of stripes or bars from spots, and in doing so must call attention to the rarity of true stripes in butterflies. By a true stripe I mean one that has even edges, that is, whose sides are uninfluenced by structure. In all our British species such as _P. machaon_, _M. artemis_, _M. athalia_, _V. atalanta_, _L. sibilla_, _A. iris_, and some of the Browns, Frittilaries and Hair-streaks, which can alone be said to be striped, the bands are clearly nothing more than spots which have spread up to the costæ, and still retain traces of their origin either in the different hue of the costæ which intersect them, or in curved edges corresponding with the interspaces of the costæ. This in itself is sufficient to indicate their origin. But in many foreign species true bands are found, though they are by no means common. Illustrations are given in Plate IV., of two Swallow-tails, _Papilio machaon_, Fig. 11, and _P. podalirius_, Fig. 12, in which the development of a stripe can readily be seen. In _machaon_ the dark band inside the marginal semi-lunar spots of the fore-wings retain traces of their spot-origin in the speckled character of the costal interspaces, and in the curved outlines of those parts. In _podalirius_ the semi-lunar spots have coalesced into a stripe, only showing its spot-origin in the black markings of the intersecting costæ; and the black band has become a true stripe, with plain edges. Had only such forms as this been preserved, the origin of the spots would have been lost to view.